1. Field of the Invention
The present invention relates generally to an internal combustion engine of the type wherein the coolant is boiled, so as to make use of the latent heat of vaporization thereof, and the coolant vapor used as a vehicle for removing heat from the engine, and more specifically to an improved coolant level sensor arrangement therefor.
2. Description of the prior art
In currently used "water cooled" internal combustion engines, the engine coolant (liquid) is forcefully circulated by a water pump through a circuit including the engine coolant jacket and a radiator (usually fan cooled). However, in this type of system a drawback is encountered in that a large volume of water is required to be circulated between the radiator and the coolant jacket in order to remove the required amount of heat. Further, due to the large mass of water inherently required, the warm-up characteristics of the engine are undesirably sluggish. For example, if the temperature difference between the inlet and discharge ports of the coolant jacket is 4 degrees, the amount of heat which 1 Kg of water may effectively remove from the engine under such conditions is 4 Kcal. Accordingly, in the case of an engine having 1800 cc displacement (by way of example) is operated at full throttle, the cooling system is required to remove approximately 4000 Kcal/h. In order to achieve this, a flow rate of 167 1/min (viz., 4000-60.times.1/4) must be produced by the water pump. This of course undesirably consumes a number of horsepower.
In order to overcome this problem it has been proposed to boil the coolant and use the vapor as a heat transfer medium (thus taking advantage of the latent heat of evaporation of the coolant). Examples of such arrangements are found in U.S. Pat. No. 1,376,086 issued on Apr. 25, 1921 in the name of Fairman and in European Patent Application Publication No. 0059423 published on Sept. 8, 1982.
However, with such arrangements a problem has been encountered in that in zones of high heat flux, such as in the immediate vicinity of the combustion chamber, exhaust port and valve, upon boiling of the coolant, extraordinarily large gas bubbles are sometimes produced. These bubbles tend to displace liquid coolant from particular areas of the coolant jacket which, due to the momentary lack of coolant, rapidly elevate in temperature giving rise to the formation of localized "hot spots". These so called "hot spots" due to their elevated temperatures tend to promote the formation of further large gas bubbles which continue to displace coolant and thus induce localized "dry outs" within the coolant chamber. This of course leads to knocking and/or thermal damage (e.g. piston seizure).
To obviate this problem it is necessary to dispose a liquid coolant level sensor relatively close to the zones of high heat flux wherein the above mentioned localized "dry outs" tend to occur so as to permit quick ascertainment of such conditions. However, due to the bumping and frothing of the coolant which accompanies the vigorous boiling in the zones of high heat flux, the level indication by such sensors is often erroneous due to the deluge of waves, foam and rain-like precipation of coolant droplets which occurs under such conditions.